Lets lead with some reality checking.
The torpedoes would have extended acceleration in the hundreds of Gs and have plenty of time to get up to stupendous speeds before they are in range of the lasers.
When people talk about the "tyranny of the rocket equation", they mean the way it stomps, hard, on stuff like this. A rocket with both stupendous force (to develop those hundreds of gravities) and stupendous efficiency (to keep running for long enough to reach those stupendous speeds) is astonishingly high tech to the point of being nigh-on-impossible. Generally speaking you get one or the other of those two things, not both.
You might be able to do it with a nuclear saltwater rocket, but even then "hundreds of gravities" seems like a bit stretch.
The torpedoes have armour specifically designed to be resistant to lasers. (You have educated me on how good real lasers are but I still don't want them to feature to heavily in my story. They feel too "clean" or something.)
Lasers powerful enough to reach out and swat things across tens or hundreds of thousands of kilometres of space laugh at armour, and small torpedoes that need to carry a big warhead and a big engine can't afford to haul much armour anyway. For a realistic scenario, you'd be better off taking an approach that simply says that powerful lasers are too big and too inefficient to be useful on a warship that isn't entirely made of heat radiators, which would then be limited in other ways.
H-Bombs slamming into the side of ships
Firstly, don't use plain old nukes. In the very best scenario, a nuke going off in contact with the hullk of an enemy, half of the energy released will be in the hemisphere facing away from the ship, and so will be wasted. Actually hitting something manoeverable that can see you coming from a million km away is far too hard to be worth trying.
Instead use Casaba Howitzer type nuclear shaped charges that can (largely) direct a nuclear blast at a target from hundreds or thousands of km away. Its an energy weapon, sure, but no-one would ever describe a focused nuclear explosion as too "clean" or "neat". Shorter ranged than lasers too.
(also, if you genuinely have torpedoes that can hit a percent of the speed of light, you might just consider using fragmentation warheads. cheaper, simpler, still pretty devastating)
Now, on to your actual question.
Is there armour that could withstand that kind of blast?
...mmmmmmaybe? Now, Casaba Howitzers grew out of the Orion project, a propulsion system that involved using nuclear blasts to push spacecraft. Obviously, said craft would need to be fairly nuke resistant. A close enough blast would still smash them, but even then the pusher plate would help. Armouring your whole ship like that is probably far too heavy and impractical but a spacecraft design that incorporated a physical shield is potentially a fun one. Big dense metal slab with generous layers of radiation-absorbing material, shock absorbers, whatever. Face towards enemy and joust with nuclear lances!
Just remember that any blast close enough will fry you. Now, if your defences are good enough, you can force incoming torpedoes to detonate too far away from you to make a one hit kill, simply by persuading its onboard computer that it will certainly be wasted if it gets any closer.
And speaking of defences,
Or Maybe a form of defence I hadn't considered?
You can see torpedoes coming. At 100km/s they'll take nearly an hour to cross a light second. At 1000km/s they'll take an hour to cross 10, obviously. Unless you're using warp drives, you'll almost certainly not get as fast as 10000km/s (0.03c), so the target has lots of time to think. Any drive system capable of pushing an object that fast in a short time is so energetic that there's no way to stealth it. The target will see you.
Now, a warship might be quite a tough thing. You need a big blast to kill it, or many small ones. A torpedo on the other hand, that has no mass to spare for significant armouring and toughness. You need waaaay less energy to mission-kill it, let alone outright destroy it.
How do you get to an incoming missile far enough away to kill it safely? Use interceptor missiles. They're related to torpedoes, so have the same incredible drive systems and can reach out to extreme range to meet their targets in short order. Interceptor missiles can use warheads that aren't much good against ships, because their targets are much softer. This makes your interceptors smaller and cheaper, or faster and/or more manoeuvrable than their targets.
- Your lasers are crap at long range, but you can use bomb-pumped lasers mounted on a torpedo to swat an enemy missile at range, faster than it can dodge. X-ray and gamma-ray lasers are impractical to armour against. Potentially more precise and perhaps even longer ranged than casaba howitzers... depending on how you like your tech you can swing it either way.
- Hitting a fleck of gravel at 1000+km/s is likely to be devastating. An interceptor could have a fragmentation warhead that projects a cone of grit towards its target. The odds of any one speck hitting a target are low, but a big cloud of probabilistic doom isn't something that you want to throw your limited numbers of expensive torpedoes into. Just get close enough to your target that the grit cloud is dense enough to be a problem. Worst case you make them waste fuel and time evading it, softening them up for the next interceptor. The cone of debris is moving away from you at speed, so it is no threat to your own counterattack or your warship itself.
- Casaba howitzer them back! Nuking nukes is a perfectly viable tactic.
Antimatter is another, uh, matter altogether. Probably worth saving for another question. Suffice to say, that whilst it is definitely very useful, it isn't really earth shatteringly gamechanging in a warhead (but useful in a rocket). Don't worry about it too much.
